1. Technical Field
The present disclosure relates to apparatus and methods for securing a first structural member and a second structural member to one another.
2. Description of Related Art
FIG. 1 illustrates one common method for securing a first structural member 1I and a second structural member 12 to one another. The first structural member 10 may be, for example and without limitation, a frame, a bulkhead, a cap or a rib. The second structural member 12 may be, for example and without limitation, a wing skin, a floor panel or a fuselage skin panel. First and second attachment angles 14 secure the structural members 10, 12 to one another. Each angle 14 comprises a first section 16 and a second section 18. The sections 16, 18 may be substantially planar, or may include some curvature. For simplicity, the sections 16, 18 are illustrated herein as being planar.
The sections 16, 18 are substantially perpendicular to one another and are joined at a radiused corner 20. The first section 16 of each angle 14 is secured to the first structural member 10, and the second section 18 of each angle is secured to the second structural member 12. In FIG. 1 adhesive 22 secures the mating surfaces to one another. However, other methods of attachment are also used, such as mechanical fasteners, bonding and co-bonding. In FIG. 1 a gap 23 is left between the first structural member 10 and the second structural member 12. The gap 23 may be filled with resin (not shown).
The method of attachment illustrated in FIG. 1 creates disadvantageous structural loading issues when pull-off loads are high. For example, pull-off loads create induced moments at the interfaces between the angles 14 and the second structural member 12 adjacent the radiused corners 20. These induced moments can cause the angles 14 to peel away from the second structural member 12. Also, impacts to the second structural member 12 in the area between the angles 14 can create fracture zones in the resin filling the gap 23. Cracks can propagate through the resin to the angles 14 causing de-bonding and bond failure.
FIG. 2 illustrates another common method for securing a first structural member 10 and a second structural member 12 to one another. As shown, a single-piece Pi fitting 24 includes a first section 26. Second and third sections 28. 30 extend substantially perpendicularly from a first face 32 of the first section 26, making the Pi fitting 24 resemble the Greek letter “Pi”. A space 34 between the second and third sections 28, 30 receives the first structural member 10. Adhesive 22 secures the first structural member 10 to inner faces of the second and third sections 28, 30. A second face of the first section 26 is secured to the second structural member 12 with adhesive 22. The space 34 may be filled with resin (not shown).
The one-piece Pi fitting 24 illustrated in FIG. 2 provides some structural advantages over the two-piece attachment angles 14 illustrated in FIG. 1. However, the Pi fitting 24 presents installation issues due to the fixed distance between the second and third sections 28, 30. For example, variances in the thickness of the first structural member 10 and/or in the distance between the second and third sections 28. 30 can cause the gap 34 to be too narrow to receive the first structural member 10, or cause the gap 34 to be so wide that it is not possible to adhere the first structural member 10 to both of the second and third sections 28, 30. Further, after applying adhesive 22 to the first structural member 10 and/or to the second and third sections 28, 30 it can be difficult to position the first structural member 10 between the second and third sections 28, 30 without disturbing the adhesive 22 and diminishing the structural integrity of the bonded area.